1. Field of the Invention
This invention relates to a composite closure for a container for the packaging of a product under at least partial vacuum, which closure includes a metal lid that has a portion whose position is altered by a loss of vacuum within the container to give a visual indication of such loss of vacuum, and a plastic ring to secure the metal lid to the rim of a container. The closure is of the push-on, twist-off type.
2. Description of the Prior Art
Many food products which are packaged in glass jars are packaged under a partial vacuum to prevent spoilage or to preserve flavor, and it is important that the closure for such a container be able to seal the container properly to maintain the vacuum in the container until the first opening thereof. It has also been recognized that it is desirable for a closure for a container for a vacuum-packed product to incorporate means which will indicate the presence or absence of the desired degree of vacuum, and the prior art is familiar with metal closures which incorporate such a feature. For example, U.S. Pat. No. 3,152,711 (G. V. Mumford et al.), which is assigned to the assignee of this application, discloses a one-piece metallic closure in which the top panel of the closure incorporates a domed central portion, which domed central portion is deflected downwardly by the presence of a suitable degree of partial vacuum in the associated container. Because of the inherent elasticity of the metal of the closure, the deflected domed central portion will return to its normal position upon the release of the vacuum and the resulting repressurization of the container, thereby providing an indication of such release of container vacuum which is detectable visually, or by various types of electro-mechanical or electro-optical types of inspection equipment. U.S. Pat. Nos. 3,062,396 (G. J. Foss et al.), 3,160,302 (G. F. Chaplin), and 4,533,059 (W. J. Kapolas et al.) also disclose one-piece metallic vacuum indicating closures that operate in a similar manner, and U.S. Pat. No. 3,836,033 (A. Pdesta) discloses a two-piece vacuum indicating closure having a metallic closure panel and a separate metallic closure panel retention skirt that otherwise also operates in a similar manner.
As is noted in U.S. Pat. No. 4,093,094 (N. J. Smalley et al.), which is also assigned to the assignee of this application, a reference which discloses a two-piece vacuum indicating closure that is useful in a home canning system, certain advantages are obtained in a vacuum indicating closure when at least the skirt portion thereof is formed from a thermoplastic material. However, the closure system of the aforesaid U.S. Pat. No. 4,093,094 requires separate handling of the metal lid and plastic ring components thereof, since the closure system of such reference does not incorporate means to positively interlock the metal lid and the plastic ring, and, thus, the use of the closure system of the aforesaid of U.S. Pat. No. 4,093,094 is not suitable for use in a packaging plate where it is necessary to mechanically apply closures to containers at a high rate of speed in order to be able meet the cost constraints that apply to any such industrial operation. Further, the plastic skirt of the aforesaid U.S. Pat. No. 4,093,094 is affixed to the finish portion of the associated container by mutually engageable helical threads, an attachment technique which has certain drawbacks for use in an industrial operation relative to closures which can be applied by a push-on action, as is described in co-pending application Ser. No. 395,397, filed on July 6, 1982, by George V. Mumford, an application which is also assigned to the assignee of this application, and in U.S. Pat. No. 3,371,813 (R. C. Owen et al.) and in British Patent Specification No. 635,262 (E. T. Webb), references which also describe various types of push-on, twist-off closures.